1. Field of the Invention
The present invention relates to a method of and apparatus for augmenting power produced from gas turbines, and more particularly, to a method of and apparatus for augmenting power produced from gas turbines in a combined cycle ground-based power plant.
2. Background Art
A combined cycle power plant is one in which the exhaust gases produced by a gas turbine are used to operate a steam boiler that produces steam supplied to a steam turbine. The power produced by such a combined cycle power plant is the sum of the outputs of the generators driven by the respective turbines. It is conventional to increase the work produced by the gas turbine by reducing the turbine inlet temperature, and by increasing the turbine inlet pressure. In the American Society of Mechanical Engineers Paper No. 65-GTP-8 (1965) by R. W. Foster-Pegg, the author describes supercharging a gas turbine (i.e., increasing the inlet pressure) by using a forced draft fan in order to increase the power output of the, turbine. The detrimental effect on the power output of the gas turbine due to the increase in inlet air temperature resulting from the fan operation is compensated for by spraying water into the air leaving the fan and before the air is applied to the turbine to bring about cooling of this air. The ambient air temperature and humidity control the effect this expedient has on the increase in power output of the turbine. Under hot, humid conditions, this technique has not proved to be effective.
In addition, gas turbines produce reduced work at high ambient temperatures due to a reduction in the mass flow of air through the system. Such high ambient temperatures, in a combined cycle utilizing a steam turbine operating on steam generated by the exhaust gases of the turbine, furthermore cause a reduction in the mass flow of exhaust gases thus reducing the work produced by the steam turbine. Even so, the effect on steam turbine performance will be partially compensated for, under high ambient temperature conditions, when water cooled condensers are used, because of the increased exhaust gas temperature. However, when air cooled condensers are utilized, high ambient temperatures will have a detrimental effect. In such case, the work produced by the steam turbine is reduced due to the lower mass flow on the gases exiting the turbine, is recovered somewhat due to the higher temperature of the gases, but is further reduced due to the higher condensing pressure prevailing in the air cooled condenser.
U.S. Pat. No. 3,796,045 discloses a gas turbine power plant in which air supplied to the compressor of the gas turbine is first passed through a motor driven fan that pressurizes the supplied air, and then through a deep-chiller which may be a conventional compression-type refrigeration unit. The net power developed as a result of this approach exceeds the net power of a gas turbine power plant without precompression and deep chilling. In another embodiment shown in the 1045 patent, a waste heat converter is provided for utilizing the heat in the exhaust gases of the gas turbine to drive the fan and the deep chiller.
Pending U.S. Pat. application Ser. No. 07/818,123 filed Jan. 8, 1992, discloses an improved chiller for deep chilling the air supply to a gas turbine. The term xe2x80x9cdeep chillingxe2x80x9d is used in this specification to mean chilling ambient air to a temperature significantly below ambient air temperature. Specifically, deep chilling refers to chilling the air to the minimum temperature considered suitable for inlet chilling in a ground-based gas turbine based power plant of the type conventionally used by utilities for supplying power to an electrical grid. Such temperature is usually about 45xc2x0 F. (10xc2x0 C.) to avoid ice-built up in the blades of the main compressor driven by the gas turbine taking into account a drop of about 10xc2x0 F. (5xc2x0 C.) in the static air temperature in the compressor inlet, and a 3xc2x0 F. (2xc2x0 C.) safety margin.
Deep chilling at installations where the relative humidity is high is not cost effective. For example, deep chillers, and evaporative chillers as well, are not used in Florida, or other humid locations on the east coast of the United States, but are very common in dry areas of California.
It is therefore an object of the present invention to provide a new and improved method of and an apparatus for augmenting power produced from gas turbines by providing a new and improved technique for precompressing and cooling hot, precompressed ambient air.
The invention provides for augmenting the power produced by a gas. turbine system of the type having a main compressor for compressing ambient air supplied to the compressor to produce compressed air, a combustor for heating the compressed air and producing hot gases, and a gas turbine responsive to the hot gases for driving the main compressor and. supplying a load, and for producing hot exhaust gases. According to the present invention, power augmentation is provided for by utilizing a direct contact heat exchanger for contacting and cooling humid ambient air with cooler water for producing cooled ambient air and warmed water, and a precompressor device for compressing the cooled ambient air to produce pressurized air that is warmer than ambient air and has a lower relative humidity. An evaporative cooler, which is supplied with the warmed water, is provided for cooling said pressurized air to produce cooled pressurized air at about ambient air temperature and relative humidity, which is supplied to the main compressor.